Muffler tubes



Sept. 10, 1957 L. M. AF'PLEGATE MUFFLER TUBES Filed April 24. 1953United States Patent MUFFLER TUBE Lindsay M. Applegate, Salem, Greg.

Application April 24, 1953, Serial No. 350,975

Claims. (Ci. ISL-42) This invention is an improvement in flexiblemuffling tubes used for internal combustion engines.

Flexible muflling tubes are already known in this art, some having beenpatented in the United States as early as 1925. These earlier types,however, have achieved only very limited adoption although the acousticprinciples exemplified therein are unquestioned. There are known also inthis art various types of mufflers with rigid walls in which the exhaustgasses pass through the mufiler unimpeded by baffles or otherobstructions. The muffling of sound therein is accomplished by the useof sound absorbing materials such as steel or mineral wools to which theexhaust gases have access through a perforated pipe passing through themuflier or by other equivalent means. The acoustic principles employedby these types of muffling appliances are used also in my presentinvention.

The principal object of my invention is to produce a mufliing tube whichwill serve efiiciently and economically as a straight-through type ofmuffler and combine therewith the recognized advantages of flexibleexhaust tubing.

A second object is to produce a muffling tube that can be readilymanufactured with conventional machines and which can readily be handledby conventional methods in repair shops.

A third object is to obtain more effective muffling and longer effectivelife of muffling tubes by appropriate spatial relationship of componentsbringing about optimum utilization of sound absorbing properties ofcomponent materials.

Another object is to provide a flexible tubular muffler which can bereadily adapted to a wide variety of engines and vehicles, even thoughmanufactured in only a few sizes, by virtue of favorable dimensionalrelationships permitted by this invention.

Other objects may be inferred from the following specificationdescribing my present invention and from the claims by which it issuccinctly defined.

My invention is illustrated in Figures 1 and 2 which are respectively alongitudinal partly sectional view of my invention and a partlysectional end view.

Figures 1 and 2 show my invention in a preferred form favorable toefliciency and desirable mechanical characteristics. A conventionalflexible tube 1 encloses two other components. The inner surface of theassemblage is a channelled spiral 2 wound with space between turns. Awinding 3 of combustion-resistant fibrous material such as asbestos orglass cord is Wound around the spiral 2 and is retained thereon by thechannel edges 4 on the outside of strip 2.

The operation of the tube as shown in Figure 1 depends on the absorptionof sound in the space between the outer tube 1 and the inner tube 2. Thefibrous material 3 provides a large surface and has a yielding structurethat promotes dissipation of sound energy. The exhaust gas inside tube 2has access to the fibrous material 3 through the spaces 5 betweensuccessive turns of the inner tube 2. The internal roughness of tube 2causes some turbulence in the movement of gas through the tube and thiscontributes also to suppression of noise but this is in addition to theabsorption of sound by the fibrous material 3 and the space in which itis placed.

2,805,730 Patented Sept. 10, 1957 The fibrous material 3 shown inFigures 1 and 2 is preferably of combustion-resistant material such asasbestos or similar fibrous material. Permeability, looseness, and largeeffective surface are important for attaining optimum conditions ofsound absorbtion.

In determining the dimensions in my invention it will be observed thatthe ordinary mufl ler is usually only about two feet long, but that thetotal length of muffler pipe and mui'fler is usually ten feet or more.The muffling effect of two feet of tube as made in this invention can beabout one-fourth or less than that of a conventional muffler and still,by virtue of the greater length employed, be as effective as theconventional mutfler. This permits the cross sectional area of the tubein my invention to be of the same order as that of the conventionalexhaust pipe. An internal diameter of one and one-half inches in tube 2for example, a radial thickness of the order of one-eighth inch in thefibrous layer 3, and an ordinary flexible tube 1 with an internaldiameter of about one and three-fourths or two inches allows a structurethat is economical, reasonably compact, and effective. The mufflingeffect of layer 3 increases with thickness and is dependent on thecharacteristics of the absorbent material used between the inside andoutside tubes.

The relative dimensions of parts and spacings shown in Figures 1 and 2are subject to design for good performance and convenience inmanufacture. The spaces 5 between the rearward edges of the turns andthe forward edges of the preceding turns in the direction of advance ofthe turns, as shown in Figure l, are required to give the gasses in thetube access to the sound-absorbent material 3. The composite tube can berolled continuously forming in succession the inner spiral 2, the spiralof soundabsorbent material 3 wound on the exterior of the turns of 2,and the enclosing flexible tube 1. The technique of tube manufacture issuch that it will ordinarily be expected that the sound-absorbentmaterial 3 will fit closely to the inside of outer tube 1. This has theadvantage of holding the three parts of the composite tube firmlytogether for handling, cutting, and attachment of fittings.

The spaces shown between the successive turns of the sound-absorbentmaterial 3 are provided to permit unimpeded access of the exhaust gasesto the sides, and, consequently, the maximum convenient area, ofmaterial 3. These spaces need not be large when the material 3 ischaracterized by an open mesh-like structure as long as the material isclean. In service, however, carbon and rust may tend to decrease thesizes of the openings and therefore they should be large enough whenfirst manufactured to provide for this.

The individual mechanical components of the composite tube shown inFigures 1 and 2 could be described in various ways but for conveniencein description, es-

' pecially in the claims, certain conventionalities applicable to thisart should be understood. The outer tube 1, preferably metallic, maywell be described as a spirally wound strip formed with interlockingedges, and this will ordinarily be understood from the usual expressionflexible tube. The inner tube or winding 2 can be a simple spiral offlat strip with the edges bent outward to form a channel as shown in thedrawing. The strip, wound with space between adjacent edges, is referredto conveniently as a spaced wound strip.

This spirally wound inner strip, when referred to as spaced, is limitedto construction in which there is ample clearance between turns forunimpeded access of gases in the tube to the sound absorbent materialwound on and parallel to the spaced turns of the inner strip. Thisdistinguishes my invention from those in which the inner tube iscomposed of over-lapping turns of strips or of other construction inwhich perforations or equivalent means are used to provide radialpassageway to the sound absorbent material for the gases in the tube.This arrangement is described in the claims as non-overlapping todistinguish the fully spaced turns from arrangements in which the stripis wound in overlapping or in inter.- locking turns as in the outer tubeof Figure l.

i The expressions concave section or channel-shaped section are used todescribe the cross-section of the strip of which the inner tube 2 iswound and to distinguish this simple cross-section of strip from themore complicated strips of S-shaped or other configurations withinterlocking edges. There is no way for the channel-shaped strip to beinterlocked. The sound absorb nt material 3 may be, for example, steelwool formed into a rape or cord-like strand. Glass or asbestos fibersformed into a rope or cord may similarly be used. This material isporous or fibrous in the sense that many interstiees and a large area ofsurface are provided to facilitate the absorption of sound. The degreeof compactness of the fibrous structure is limited to that which willpermit mechanical displacement and friction between the fibers topromote the dissipation of the sound energy. This material isconveniently described as sound absorbent. The wound material 3 isreferred to as a strip of sound absorbent material which, of course, asan expression, may include the cross-sectign of a round cord as well asany other convenient cross-section.

I claim:

1. A muffling tube comprising a non-overlapping channel-shaped stripspirally wound with separation between adjacent turns of the strip, therearwardedge of each turn of the spirally wound channel-shaped stripbeing spaced from the forward edge of the preceding tm'n in thedirection of advance of the turns, a spirally wound strip of porousmaterial of approximately the width of the channel of saidchannel-shaped strip wound parallel and out side said channel-shapedstrip and retained thereon by the externally disposed channel edgesthereof, and a substantially gas-tight flexible interlocking-wound-striptube concentrically enclosing said channel-shaped strip and said porousstrip.

2. A flexible tube comprising a spaced-turn spiral of non-overlappingchannel-shaped strip with the channel edges outward, the rearward edgeof each turn of the spiral ofc'hannel-shaped strip being spaced from theforward edge of the preceding turn in the direction of ad- Vance of theturns, a spaced-turn spiral of fibrous strip wound on and parallel tothe said spiral of channel-shaped strip, and occupying substantially thefull width thereof,

and a flexible tube "concentrically enclosing said, spaced wound strips.

3. The combination of an inner tube formed of spacednon-overlappingstrip, spirally wound with the rearward edge of each turnbeing spaced from the forward edge of the preceding turn in thedirection of advance of the turns, a strip of fibrous material aroundsaid inner tube, and a substantially gas-tight flexible tube.concentrically enclosing said inner. tube and fibrous material, saidspaced non-overlapping strip being channel-shaped with the channeloutward to hold said fibrous strip in place in said channel, saidfibrous strip being wound on and parallel to the turns of said innertube strip.

'4, A composite tube comprising an outer tube of spirally woundresilient flexible strip formed withinterlocking edges, an innerconcentric spiral of non-overlapping resilient flexible strip,channel-shaped on the exterior of the spiral, wound, with space betweenadjacent turns, the rearward edge of, each turn of the inner spiralbeing spaced from the forward edge of the preceding turn in thedirection of advance of the turns, and a spirally Wound strip ofsound;absorbent material between the outer tube and inner. wound spiral,wound to lay in the channel on said inner spiral strip, and retained incontact with theedges of said channel.

5.. A composite, tube comprising an outer tube of spirally wound stripformed with interlocking edges, an inner concentric spiral ofnon-overlapping strip, formed with out-turned edges, wound with spacebetween the adjacent edges of successive spiral turns, the rearward edgeof each turn of the inner spiral being spaced from the forward edge ofthe preceding turn in the direction of advance of the turns, and aspirally wound strip of sound-absorbent material between the outer tubeand the inner spiral strip, on said strip, and in contact with theout-turned edges thereof.

6. A composite tube comprising an outer tube of spirally wound stripformed With interlocking edges, an inner concentric spirally woundnon-overlapping strip whose edges are turned outward to form a channelwith space between the edges of adjacent spiral turns, the rearward edgeof each turn of the inner strip being spaced from the forward edge ofthe preceding turn in the direction of advance of the tu ns, and a stripof porous material spirally wound in said channel on the outer side ofsaid inner spirally wound strip, said porous strip being substantiallythe full width' of said inner spiral strip and retained thereon byout-turned sides of said channel.

7. A composite tube comprising an outer spirally wound strip formed withinterlocking edges, an inner concentric non-overlappingchannel-shapedstrip spirally wound with space between the edges ofadjacent spiralturns, the rearward edge of each turn of the inner stripbeing spaced from the' forward edge of the preceding turn in thedirection of advance of the turns, and a strip of porous material woundtherewith and secured in place by being wound in the channel presentedon the exterior of said inner spiral.

SfAcomposite tube comprising an outer spirally wound strip formed withinterlocking edges, an inner concentric s irally wound non-overlappingstrip of channel-shaped cross-section, the rearward edge of each turn ofthe inner spirally wound strip being spaced from the forward edge of thepreceding turn in the direction of advance of the turns, and acombustion-resistant, sound-absorbent strip Wound between the inner andouter strips retained by the channel on the exterior of said innerstrip.

9. A composite flexible tube comprising an outer flexible tube formed ofa spirally wound flexible metallic strip with interlocking edges, aninner concentric tube formed of a spirally wound flexible metallic stripwith space between the adjacent edges of successive turns, the rearwardedge of each turn of the tube being spaced from the forwardedge of thepreceding turn in the direction of advance of the turns, said inner tubestrip having outturned edges forming a channel thereon, and asoundabsorbent, combustion-resistant coil of material of ap proximatelythe width of said channel wound between the outer and inner tubes aroundand parallel to the turns of said inner tube strip.

10, A composite tube. comprising an outer tube of spirally wound stripformed with interlocking edges, an inner concentric spiral ofnon-overlapping strip, formed with at least one out-turned edge, woundwith the rearward edge of each turn of the inner spiral strip beingspaced from the forward edgeof the preceding turn in the direction ofadvance of the turn, and a spirally wound strip of sound-absorbentmaterial between the outer tube and the inner spiral strip, on saidstrip and in contact with said gut-turned edge thereof.

References Cited in. the file of this patent UNITED STATES PATENTS1,530,324 Pribil Mar. 17, 19.25

2,014,368 Blundell Sept. 17, '1935 2,073,951 Servais Mar. 16, 19372,718,273 Dehaus Sept. 20, 1955 FOREIGN PATENTS 703,130v Germany Mar. 11941 $3 ,110 Great Britain" July 31, 1944

